It is known to increase the power of an internal combustion engine by compressing the air, which is needed for the combustion of the fuel, by means of an exhaust-gas turbocharger. The exhaust-gas turbocharger includes a turbine and,a compressor operated by the engine in the air intake manifold. Exhaust-gas turbochargers, especially in motor vehicle drive systems, have the disadvantage of a delayed and inadequate response performance at low rpms of the engine. To improve the response performance of the exhaust-gas turbocharger, it is known to support the exhaust-gas turbocharger by means of an electric auxiliary drive. This can be achieved, for example, with an electric motor integrated into the exhaust-gas turbocharger. This motor supportingly drives the shaft of the turbocharger at low rpms of the engine. This, however, causes a high rpm loading of the electric motor as well as a high requirement on electric power because of the high mass inertial torques of the turbine of the exhaust-gas turbocharger.
To avoid these disadvantages, it is, for example, known from U.S. Pat. No. 6,029,452 to operate an electrically operated charge air compressor in the air intake manifold in series with a conventional exhaust-gas turbocharger. The charge air compressor is also referred to as an electrically operated auxiliary charger. This arrangement affords the advantage that the electrically operated auxiliary charger can be optimized to the lowest rpm range of the internal combustion engine, and the power requirement of the auxiliary charger is clearly less because of the significantly lower mass moment of inertia. The electrically operated auxiliary charger is utilized separately in the air intake manifold.
German patent publication 101 24 543 discloses a method and an arrangement for controlling an electrically operated charger which cooperates with an exhaust-gas turbocharger for compressing the air supplied to the engine. The drive of the electric charger takes place via a drive signal which is formed in dependence upon a pregiven value for the compressor pressure ratio of the electric charger.
German patent publication 197 40 968 discloses the determination of a desired value for the air mass flow in the intake manifold in dependence upon the driver command. From European patent publication 885 353, it is known to determine a desired throttle flap angle and a desired charge pressure value on the basis of the desired charge derived from the driver command.
It is an object of the invention to provide a method and an arrangement for controlling a charger which affords the advantage with respect to the foregoing that the drive signal is formed in dependence upon a first operating state of the engine, which directly precedes an increase of the driver command torque, in such a manner that the charger increases its rpm already during this first operating state. In this way, the charger already runs up before its auxiliary compression is needed to realize the increased driver command torque. In a subsequent second operating state for increasing the driver command torque, the required target rpm of the charger is reached more rapidly, that is, the increased driver command torque is more rapidly realized. The increase of the rpm in the second operating state from the increased rpm, which is reached already in the first operating state, to the target rpm imposes also a lower load on the on-board electric system. A positive regenerative effect results with a coaction of the charger and the exhaust-gas turbocharger for compressing the inducted air of the engine. The positive regenerative effect has the consequence that the exhaust-gas turbocharger also runs up with the increase of the rpm of the charger in the first operating state. In this way, the increased driver command torque is still more rapidly achieved in the second operating state.
It is especially advantageous when the first operating state is achieved with the actuation of a clutch. In this way, the clutch actuation can already be used in a start-to-move operation or in advance of an acceleration operation for running up the rpm of the charger. In a vehicle having an automatic transmission, the first operating state can be detected by the release of the brake pedal by the driver""s foot (detectable, for example, by the opening of the brake switch) while a drive stage is set. The torque of the engine, which is requested by the driver (that is, the driver command torque) is reached in this way more rapidly during a start-to-drive operation or an acceleration operation.
A further advantage is that with the increase of the rpm during the first operating state, a first bypass is opened with this bypass being connected in parallel with the charger. In this way, no compression is effected by the increase of the rpm of the charger in the first operating state and the load on the on-board electrical system is thereby considerably reduced. In the first operating state, there is a free run-up of the charger without load.
What is especially advantageous is that in the configuration of the charger as an electric auxiliary charger, during the first operating state, the rpm of the electric auxiliary charger is increased to a pregiven value and/or is increased at a pregiven slope and that the pregiven value for the rpm is formed in dependence upon the formation of the rpm of the electric auxiliary charger for at least a previous increase of the driver desired torque. In this way, the pregiven value for the rpm can be adjusted in dependence upon the type of driver or in dependence upon the driver behavior.
A further advantage is that, during the first operating state, a torque reserve is formed. In this way, the switch-on jolt for a switch-on of the charger is compensated in a first operating state.
A further advantage is that the torque reserve is formed in dependence upon the formation of the rpm of the electric auxiliary charger for at least a previous increase of the driver command torque. In this way, the torque reserve can be adjusted in dependence upon the type of driver or on the driver behavior.
A further advantage is that, in the first operating state of the engine, an operating variable (especially an engine rpm) of the engine is estimated for the subsequent second operating state and that the rpm of the electric auxiliary charger is increased in the first operating state when the estimated operating variable lies in a pregiven operating range. In this way, substantially the entire duration of the first operating state can be utilized for increasing the rpm of the electric auxiliary charger so that, with the start of the second operating state, the target rpm of the electric auxiliary charger can be reached more rapidly and with lower load on the on-board electric system starting from the already increased rpm of the electric charger which is already reached in the first operating state. The target rpm is required to realize the increased driver command torque.
A further advantage is that the estimation of the operating variable is carried out based on a set gear stage of a transmission which is to be expected in the subsequent second operating state. In this way, the estimate of the operating variable can be carried out especially simply especially for a first operating state configured as a shift operation.
A further advantage is that with the configuration of the charger as a mechanical auxiliary charger, the drive signal can be formed during the first operating state so that a shift clutch of the mechanical auxiliary charger is closed to a crankshaft of the engine. In this way, an accelerated arrival at the target rpm can be achieved in the second operating state for the mechanical charger. Furthermore, a switch-on jolt of the mechanical charger is considerably reduced in the second operating state and is undertaken in the first operating state. This increases driving comfort.
A further advantage is that, during the first operating state, a second bypass is closed which is connected in parallel to the mechanical auxiliary charger. In this way, the charge pressure or the compressor pressure ratio of the mechanical auxiliary charger is already built up in the first operating state so that an increased charging pressure is already present at the start of the second operating state and the target rpm of the mechanical auxiliary charger is reached even more rapidly.
Furthermore, with this measure, the switch-on jolt of the second operating state is further reduced and the driving comfort increased.